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Crime Scene and DNA Basics for Forensic Analysts


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Since each VNTR region consists of repeats of a specific sequence of bases, complementary oligonucleotides can be synthesized.  These oligonucleotides, when labeled with a marker such as P32 or a chemiluminescent compound, are known as probes

There are five basic steps to developing DNA profiles using VNTRs:

  1. Extracting DNA
  2. Cutting DNA into fragments using restriction enzymes
  3. Separating the fragments based on size using gel electrophoresis
  4. Transferring the fragments to a nylon membrane (southern blotting), causing immobilization
  5. Locating and identifying the fragments by applying a solution containing the probe of interest, which then hybridizes to the immobilized DNA. Visualization of the fragments requires a lengthy exposure of the probe to a detection system and can add several days to the assay time.
Example of 16-base pair tandem repeats in the D1S80 locus.
Example of 16-base pair tandem repeats in the D1S80 locus. The sequence is usually repeated between 14 and 40 times.
National Institute of Justice (NIJ) (see reuse policy).

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